Hammer - Run duration

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Raj,

Are you saying that you're seeing more severe negative pressures when you increase the total simulation duration? Make sure you're looking at an animation of a profile of the system in the transient results viewer, with the "generate animation data" calculation option set to True.

communities.bentley.com/.../using-profile-animation-to-better-understand-transient-results-in-hammer

By looking closely at the animation, it may be more clear as to why this is happening. It could be that a vapor or air pocket in the system collapses later on in the simulation, which can result in severe surges.

If this doesn't help, please send the model per Sushma's reply.

How to determine the run duration, when i go for 10L/a or so the min. transient pressure is exceeding the shutoff head of pump.

Hi Raj,

The transient simulation duration would typically be set long enough so that you observe the full transition from the starting steady state to the ending steady state. See more in the Help topic called "Determining the Transient Run Duration".

With that said, it sounds like you are having a problem with the transient results for a pump toward the end of a long duration. What is your transient pump type set to? (are you simulating a pump startup, emergency pump shutdown, something else?

Note that the transient simulation uses a four-quadrant curve (based on your selection of Specific Speed), not the pump definition that you entered, when the pump type is set to pump start or shut down. The pump definition influences the nominal operating point that the four-quadrant curve is built around. This means that the pump may not exactly follow the pump curve you entered. There's some additional information here:

communities.bentley.com/.../11090.how-are-the-pump-flows-used-in-the-transient-analysis-derived-in-hammer

...and in the section called "Why is the Transient Simulation not Settling Exactly on the Nominal Head/Flow I entered?" here:

communities.bentley.com/.../3276.modeling-a-pump-start-up-transient-event-in-bentley-hammer-v8i-tn

If this does not help, please zip and send a copy per Sushma's instructions. Please be sure to provide the name of the zip file on this forum thread. Also please be sure to provide details on the steps to follow to observe the problem, and what you expected and why.